This invention relates to an elevator constituted by a plurality of telescopic sections, positively guided on one another, and to a locking device therefor.
In a known elevator of this type, each telescopic section is formed as a ladder, and is lockable against retraction with respect to the adjacent telescopic section, in several positions of extension, by means of a respective locking device. Each locking device includes at least one cable-actuated, spring-loaded, pivotable locking dog. Each locking dog is provided with a support member for the adjacent telescopic section. The locking dogs are actuated by draw cables which actuate locking cables attached to movably mounted intermediate members.
DE-PS No. 3 001 410 describes an elevator of this type, the elevator comprising a rail for the guidance of a load container. In this case, on actuation of a winch, several telescopic sections are extended, moving in relation to one another. An actuator is provided at an operating position, the actuator acting via a corresponding draw cable to actuate the locking device which locks all the telescopic sections together. Locking, is thus, effected through a manually-actuated draw cable. After the locking has been released by the same draw cable, the locking device remains, under spring loading, in the unlocked position. For the transmission of the cable traction from one telescopic section to the next, pivotable bodies are used which permit only a slight "shortening" of each cable. In this case, it is disadvantageous that a considerable force must be applied for the actuation of the pivotable bodies, while only a slight shortening of the draw cable is possible. This causes an imprecise response of the locking system, because the cable shortening caused by the pivotable bodies is largely compensated by the cable stretch of the draw cable, which is substantially longer than the locking cable. This major cable stretch does not exist in the shorter locking cable.
DE-OS No. 2 519 513 describes a sliding ladder which consists of a lower ladder and an upper ladder. The relative displacement of the two ladder parts takes place by cable actuation, but by hand. In this case, a pivotable snap-in lever is mounted on the lower ladder, which remains at rest. The pivotable snap-in lever is of two-armed formation, the support face of one arm engaging under a side of the lower ladder, and the support face of the other arm engaging under the respective side of the upper ladder. During displacement of the upper ladder in the direction of extension, the snap-in lever can move aside against the force of a spring. In order to release the locking device, the draw cable must be brought into a position situated laterally of the lower ladder. Thus, this is not a suitable arrangement for locking the telescopic sections of an elevator. Moreover, in order to retract this ladder, it is firstly necessary to relieve the locking device (by raising the upper ladder by a specific amount), so that the locking device can pivot into the unlocked position. The locking device of this ladder is, therefore, usable only with relatively light sliding ladders.
The aim of the invention is to provide an improved version of the elevator and locking device described in DE-PS No. 3 001 410. In particular, it is an object of the invention to make a locking device still simpler and more reliable.
Another object is to ensure that the cable guidance necessary for the actuation of the locking device should be of such configuration that a reliable response of the release cable (and thus of the unlocking of the device) is guaranteed.
Yet another object is that the actuation of the locking device should be achieved with the minimum expenditure of force.
A stilll further object is to compensate for the differing lengths of the draw cable and of the locking cable (and the consequent differing cable elongation under stress) by a "mechanical advantage" between the two cables.